Rapids clubtail (Gomphus quadricolor) COSEWIC assessment and status report: chapter 4

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Distribution

Global range

The range of Gomphus quadricolor includes Ontario and 25 states in the United States but there appear to be large areas of unsuitable habitat within this range where the species does not occur. The global maximum extent of occurrence encompasses about 1.7 million km². Most populations are in the U.S. Midwest but its range extends from northern Alabama and Georgia to southern Ontario and from Maine, west to eastern Minnesota (Figure 3). Populations have been discovered in Ontario and several states in recent years. It is extirpated from Illinois, where the species was originally described (Tim Cashatt pers. comm. 2007). Gomphus quadricolor is probably most common in northern Wisconsin (30 counties; William Smith pers. comm. 2007), Ohio (17 counties; Robert Glotzhober pers. comm. 2007), and Minnesota (6 counties; Richard Baker and Wayne Steffens pers. comm. 2007).

Figure 3. Distribution of Gomphus quadricolor in North America (based on Donnelly 2004).

Canadian range 

The known historical Canadian range of Gomphus quadricolor consists of four rivers in southern and eastern Ontario: the Thames, Humber, Credit and Mississippi (Figure 4). Walker (1958) collected adults and larvae near Erindale on the Credit River between 1926 and 1939. He also collected exuviae on the Humber River near Kleinburg in 1939. There were no subsequent known Canadian records until 1989, when the species was collected on the Thames River between London and Ingersoll. In 2001, Gomphus quadricolor was discovered on the Mississippi River at two locations 8 km apart (Catling and Brownell 2002). The Credit, Humber, and Thames rivers are in the Mixedwoods Plain Ecozone, while the Mississippi River site is on the border between the Boreal Shield Ecozone and the Mixedwood Plains Ecozone (Environment Canada 2007). The Boreal Shield has a colder climate and typically shallower soils over Precambrian granitic bedrock. The Mixedwoods Plain has a greater proportion of hardwood tree species, but has been largely cleared since the early 1800s.

No Gomphus quadricolor were detected on the Thames or Credit rivers during a 2005 survey or in several other surveys (P. Catling, P. Pratt and others) of these rivers over the past decade and these populations are believed to be extirpated (Harris and Foster 2006). The Humber River population was extant in 2005 (Harris and Foster 2006). A survey of potential habitat on the Sydenham, Ausable, and Grand rivers in 2005 and a search of the Ontario Odonata Atlas database (2005) found no additional sites for the species.

The Humber River site extends over about 4.5 km of river. The Mississippi River sites where adults have been observed include a 50 m long stretch of rapids at Pakenham and a 200 m long rapids at Blakeney Rapids (Catling and Brownell 2002).The two Mississippi River sites are treated as a single occurrence since they are connected by a continuous stretch of river habitat with a minimum separation distance of less than 10 km (NatureServe 2007). In the Humber, only adult males were observed. Females are difficult to detect because they disperse to forest cover after emerginG. Both sexes have been observed at the Mississippi River.

The maximum extent of occurrence (EO) in Canada (including the Thames and Credit sites) encompasses 94 km² in a narrow strip 460 km long and up to 34 km wide. The maximum area of occupancy (AO) encompasses 26 km² consisting of an 800 m zone on either side of the river length occupied by the species (800 m is the approximate maximum known dispersal distance inland for Gomphus quadricolor).

Figure 4. Distribution of Gomphus quadricolor in Canada.